Traditionally, there are known vehicle motion control systems that use the curve information within a car navigation system or a turning lateral acceleration of a vehicle equipped with the motion control system, to slow down the vehicle so that an actual lateral acceleration applied thereto is likely to exceed a previously set value (for example, Patent Document 1).
In such a control device (system), in order that a magnitude of the lateral acceleration occurring when the vehicle moves past the curve will not exceed the previously set value, a target speed of the vehicle during the passage through the curve is set from a curvature of the curve present ahead, as well as from the previously set value of the lateral acceleration, and a necessary negative acceleration is created from the target vehicle speed and an actual speed of the vehicle. This method of creating the negative acceleration is effective for suppressing divergence from the road if the vehicle needs to approach a curve in excess of a maximum speed at which the vehicle can negotiate the curve.
However, if the particular setting of the lateral acceleration is a driver-set lateral acceleration that the system is estimated to permit for a usual turn, not a critical lateral acceleration, and the driver executes deceleration control in front of the curve, then the deceleration will not necessarily match the driver's feeling of slowdown. One reason for this mismatch is that although the foregoing negative-acceleration creating method based on the target vehicle speed is effective for defining a total amount of deceleration (an integral value of the negative acceleration) occurring before the approach to the curve, that method does not allow time-varying changes in the negative acceleration to be defined.
If deceleration control is conducted for constant negative acceleration in front of the curve, the deceleration obtained is likely to mismatch the driver's feeling of slowdown, depending on characteristics of the curve or on the vehicle speed. In addition, if setting the time-varying changes in the negative acceleration is attempted, this requires an unfathomable matching workload and vast volumes of data.
For example, Patent Document 2 and Non-Patent Document 1 propose, as methods of defining time-varying changes in the (positive) acceleration/negative acceleration that matches a driver's feeling of slowdown, methods of creating the (positive) acceleration/negative acceleration based on lateral jerk due to the driver's operations. These methods allow the driver to accelerate/decelerate the vehicle in substantially the same manner as a skilled driver, without setting the time-varying changes in negative acceleration on a curve-by-curve basis.